February, 1996 ^. Volume 19, Number 1

By now everyone should be aware of the satellite conference on "Practical Solutions to Odor Problems" Scheduled for airing on March 13. This conference is jointly sponsored by the National Pork Producers Council, PORK 96 and Pioneer Hi-bred International, Inc.

According to information released by the sponsors, this two hour conference will be shown from 7:00 to 9:00 pm CST, that's 6:00 to 8:00 pm here in North Carolina. Information scheduled to be presented will include:

• practical tips on reducing odor based on your specific type of production or storage facility tips on improving neighbor relations
• efficient methods to apply nutrients to land
• opportunity to call in questions to a panel of swine odor specialists during the final 30 minutes of the telecast.

Registration for this satellite conference is a modest amount of $15.00 and can be completed by calling 1800-344-4040. Those of you without your own satellite dish will be provided information on a satellite downlink site near you.

Payment of the registration fee will also provide you with a very helpful workbook that contains very valuable information on odor issues and how to deal with them.

Charles Stanislaw

Jim Barker

Introduction

As the technology of rearing weaned pigs has improved, producers have been able to wean pigs at progressively younger ages. In earlier years, when weaning age was reduced from 56 days to 28 days, there was a large and significant increase in pigs per sow per year. As some producers have moved from 28 days weaning down to 21 days, and even down to 14 days (or younger) increase in sow productivity has not always been as evident.

How large an increase can be expected by decreasing weaning age, for example, by seven days? Under the basic assumption of a gestation length of 114 days, weaning age of 28 days, 9 pigs weaned per litter, weaning to rebreeding interval of 5 days, and overall farrowing rate of 85%, the pigs per sow per year is:

If weaning age is reduced to 21 days and all other parameters remain constant, the p/s/y becomes 19.96. Likewise, reducing weaning age to 14 days gives 20.96 p/s/y. The increase in p/s/y in this scenario is 1.0 pig per day sow per year for each 7 day reducing in weaning age, assuming all other variables are not affected by weaning age. We know, however, that these variables are affected by weaning age. The return to estrus of early-weaned sows will likely be increased and their conception and farrowing rate will decrease adding non-producitive days and reducing the P/S/Y yielded by this theoretical equation.

The Process of Rebreeding

Many physiological processes must resume funtion post partum for a sow to return to estrus postweaning and conceive. Upon weaning, sows must (Britt, 1995):

1. Be able to grow mature ovarian follicles to produce estrogen to cause heat.
2. Be able to show heat in response to increased levels of estrogen.
3. Be able for the estrogen to induce an ovulatory surge of LH.
4. Be able for the mature follicles to ovulate in response to the elevated LH.
5. Be able for the uterus to transport sperm and eggs and for embryos to develop normally.

Lactation in the sow has the effect of interfering with process #1 by inhibiting the secretion of follicle-stimulating hormone (FSH) and luteinizing hormone (LH). When pigs are weaned and lactation ceases, the process is again activated and it continues through the complete cycle. This is true when weaning occurs at four weeks of age or later. The process still proceeds reasonable well with three-week weaning. However, as weaning age goes below three weeks of age, the normal course of events are increasingly disrupted by physiological responses that reduce reproductive efficiency.

These responses are (Britt, 1995):

• Sows weaned at less than two weeks of age frequently develop cystic follicles because they are not able to elicit an ovulatory surge of LH to cause the follicles to ovulate.
• Although sows can show normal heats by at least two weeks after farrowing, many of these heats are infertile because no ovulation occurs.
• Uterine involution is required for fertility to be restored. In general, two weeks are required for the uterus to involute substantially and a 3-week period is required for involution to be complete.

The Net Effect

Measuring the net effect of early weaning on pigs/sow/year is actually a complex problem. Not only is there the direct effect on litter size, but also the effect on extending the interval from weaning to rebreeding plus the effect of an increase in culling on the average parity of the herd. If the question being asked in the effect on annual net profit, then parameters such as post-weaning mortality, cost of nursery feed, cost of lactation feed, facility cost and perhaps others need to be included.

Much of this information must come from retrogressive analysis of the production records of commercial production units . Several of these studies have appeared, notably by Te Brake (1978) and more recently by Culbertson and Mabry (1995).

In the later study, PigCHAMP records were used from 13 commercial herds. These records came from 1985 to 1995 and represented a mix of environment and genetics. in all there were 138,964 usable litter records that included:

• 44,606 parity 1 sows
• 31,902 parity 2 sows
• 62,456 parity 3 sows

These results of this study can be summarized as follows:

• Effect of litter weaning weight on weaning to first service interval was relatively small
• Lactation length across all parities had a pronounced effect on weaning to first service interval with the shortest interval at approximately 25 days of lactation
• First service farrowing rate increase as lactation rate increases

The Te Brake study extended beyond the weaning to first service interval and reviewed the effect of lactation length on pigs per sow per year. It was noted, for example, that as weaning age decreased culling level increased slightly. This, in turn, affected the parity makeup of the herd by increasing the proportion of first parity litters. Taking all this into account, Te Brake estimated that the highest number of 20 kg pigs was produced in herds with lactation lengths of 21-25 days and only slightly lower with 16-20 days lactations (Table 1)

The Bottom Line

As these two studies show, early weaning is not without its negatives. In the range of weaning ages normally used by the industry today, the advantages in pigs per sow per year by earlier weaning is not large. However, there may be other advantages to earlier weaning, such as improved herd health with segregated early weaning. Even so, Vinson (1995) estimated that the return on investment and the cost of production by utilizing early weaning was relatively small (Table 2).

Charles Stanislaw

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Last modified August 5, 2000.